The present invention relates generally to bearings of the type which are radially interposed between two relatively rotatable parts and comprise an inner bearing surface engaging one of the parts and an outer bearing surface engaging the other part.
Such a bearing is used in particular in torsion damping assemblies comprising at least two coaxial parts relatively rotatable within predetermined limits of angular displacement and resilient means circumferentially interposed between the coaxial parts opposing such relative rotation. The resilient means are radially interposed between two portions of the respective coaxial parts, for example, a hub for one of the coaxial parts and a web, flange or guide ring for the other coaxial part.
As is known such a torsion damping assembly is part of a clutch plate or driven plate of an automotive friction clutch. In this environment one of the coaxial parts is fixed for rotation with a first shaft, in practice the driving shaft, in particular the output shaft of the engine of the vehicle, and the other coaxial part is carried by a hub adapted to be fixed for rotation with a second shaft, in practice the driven shaft, which is the gear box input shaft.
Such a torsion damping assembly provides filtered torque transmission between the coaxial parts when torque is applied to one of the coaxial parts. In other words the circumferentially acting resilient means filter vibrations which may develop along the kinematic chain in which it is arranged, which kinematic chain runs from the engine to the axles of the motor vehicle.
In such a torsion damping assembly, the bearing has the function of centering one of the coaxial parts relative to the other, while avoiding direct contact between the portions of the coaxial parts between which they are interposed. But in service each of the coaxial parts is centered by the shaft to which it is fixed for rotation. Thus, in a motor vehicle clutch plate, this means the engine output shaft and the gear box input shaft. In at least some arrangement these two shafts are not centered relative to each other, and there may be a certain degree of misalignment.
Accordingly, the bearing interposed between the two coaxial parts of the torsion damping assembly may under the effects of relative radial displacement between the coaxial parts be subjected to not insubstantial radial stresses which may be the source of additional spurious friction.
This additional, spurious friction may be sufficient to cancel the action of the circumferentially acting resilient means between the coaxial parts which normally have relatively low stiffness.
Whereupon, in an automotive clutch plate environment, the vibrations which develop when the vehicle idles, commonly known as dead point noise, are not correctly filtered.